Ceramic coated article



Aug. 13, 1940 w, sco 2,211,170

CERAMIC COATED ARTICLE Filed Sept.-l8, 193

wm/m W J SCOTT Patented Aug. 13, 1940 CERAMIC COATED ARTICLE Walter J.Scott, Hiiisdale, Ill., assignor to Western Electric Company,Incorporated, New York, N. Y., a corporation of New York ApplicationSeptember 18, weas l-m No. 164,472

3 Claims.

This invention relates to methods of making ceramic coated articles andmore particularly to methods of making articles having a contrasting 1ycolored coating of vitreous enamel.

The present invention is particularly adapted to the production ofmulti-eolor or ornamental enamel coatings, such as those used on signsand similar articles. In the usual manufacture of this type of product,variously colored enamels w are applied successively to a base and thearticle is fired after the application of each color. This process hasbeen troublesome because retiring tends to -damage the previously fusedenamel and thus detract from the utility of the article. An object ofthis invention is to provide improved methods for producing an, articlehaving a protective and durable enamel coating.

In accordance with one embodiment of this invention, an improved processis provided for applying a multi-color enamel coating on a number platefor telephone dials. A ring-shaped base is formed of iron and coatedwith copper and nickel. A white enamel-of suitable composition isprepared for application on the base by pulverizing, sifting and washingoperations to eliminate all particles not included within apredetermined size range. grains of white enamel are fused on the faceof the ring and the characters and design are printed thereonwith enamelpowder of contrasting colors mixed with a suitable vehicle after whichthe article is retired to mature the characters.

A more complete understanding of the invention may be had by referenceto the following description, taken in conjunction with the accompanyingdrawing, in which Fig. 1 is a. plan view of a number plate embodying theinvention, and

Fig. 2 is an enlarged sectional view of the number plate taken on theline 2-2 of Fig. 1.

In producing a number plate in accordance with this invention, a sheetof iron, steel or other suitable material is formed into a ring or base5. Because only the face of the number plate is covered with enamel, itis desirable to protect the rest of the base against corrosion and thisis conveniently accomplished by providing the entire base with anelectrodeposited protective coating before the enamel is applied. Apre-- ferred coatingincludes a layer of copper 6 on the iron and a layerof nickel 1 over the copper, which protects the unenameled portion ofthe base and also bonds satisfactorily with the subsequently appliedenamel. If onlya copper plating is applied over the iron base, thecopper tends to The sized particles or,

Q to be uniform in color, unblemished and unbroken in the finishedproduct and while these qualities oxidize and burn off during the fusingof the subsequently applied enamel, while nickel in direct contact withthe iron tends to form gases which cause a. blistering of the enamelcoating. These difliculties are avoided by use of the comgrams of copperper square inch are plated on the base and about 20 milligrams persquare inch of nickel are electrodeposited over the copper.

To complete the number plate, a coating of m white enamel andidentifying characters areapplied on the face of the base over thenickel. The white enamel 8 is applied first and used at a suitabletemperature. Letters 9, numbers l0, and a 15 background i I are thenapplied to the used white enamel in contrasting colors. The charactersand markings are formed in ceramic ink, which comprises colored metallicoxides or ceramic enamel particles mixed in a vehicle such as lin- 20seed oil. The ink ingredients are mixed to a tacky consistency toprevent running and applied on the enamel surface by means of suitabledies in either a direct or an ofiset printing process.

' The background, which may be blue or black, 25 is applied first andthe plate is then placed in an oven and baked at a temperature of about300 F. to harden the ink so that it will not be marred in subsequentprinting operations. The letters, which are usually black, are thenprinted on the number plate which is then again baked at a temperatureof about 300 F. The numerals are usually colored red and are applied inthe same manner, after which the entire plate is again fired to fullymature the ceramic ink which 35 requires a temperature around 1300" F.for approximately 4.5 minutes. I I In these operations, the repeatedfirings tend to damage the white enamel applied initially to the base.It is necessary for the white surface 40 can be provided readily in theenamel as initially fired when the usual materials are employed,refiring tends to cause blistering and re- 45 boiling which developsarough, discolored surface that is unsatisfactory in service. Coatingenamels. such as the white enamel used on humber plates, are generallyapplied either in the form of dry powder or by a wet process in which 0the enamel particles are mixed with water and a flotation agent such asclay. For both of these methods, it has been customary to employ anenamel that is comminuted to a specified maximum particle size. Inmanufacturing the enam- 55 el, the pulverizing operation is usuallyprolonged to eliminate oversize material and this practice produces avariety of particle sizes within the maximum limits, This condition hasbeen considered beneficial, particularly in wet processes where thevariety of particle sizes and a high percentage of very fine materialpromotes uniform distribution of the enamel in the liquid vehicle.

However, it has now been discovered that in processes where reflring ofthe enamel is necessary, wide variations in particle size isdetrimental. It appears that when the usual material is used, interiorair pockets are sometimes formed in the enamel body during the initialfiring, due, possibly, to early melting of the smaller particles. Thesurface of the enamel may be unbroken and satisfactory asinitiallyfired, but when the article is heated in the initial stages of refiring,the unequal expansion of enamel and metal causes cracks to form in theweaker spots, that is, through the air pockets. The cracks are filledwith air, which may be entrapped as the article becomes hotter, and thesurface of the enamel becomes plastic. During the final stage ofrefiring, the entrapped air expands and causes surface blisters orbreaks through to fracture the surface. This action may also force smallparticles of the undercoating or metal oxide from the base to the enamelsurface to impair its appearance and this phenomenon is known asreboiling. Usually the retiring temperature is insufiiciently high orprolonged to cause a final fusing over of the blistered, broken ordiscolored portions of the surface and these defects therefore remain inthe finished product.

These dimculties have been eliminated by the adoption of an enamel whichis processed before application to eliminate all particles outside of apredetermined size range. For use on number plates and similar articles,a lead boro-sllicate enamel opacified with arsenic oxide is satisfactoryfor the white cost. In accordance with this disclosure, the enamel ispulverized in a mill and the resultant particles are screend through a120 sieve. All oversize material is rejected for regrinding andundersized particles are removed from the residue by additional sifting,washing,

'- or by an air separation process.

- after the initial sitting.

It is primarily desirable to remove practically all the fine particlesas their presence appears to cause the surface defects on refirlng. Thiscan be done conveniently by washing the enamel In one satisfactorymethod, 15 pounds of ground enamel were placed in a 3 gallon jar, thejar filled with water'and the supernatant liquid decanted aftersettling. Before decanting, the jar contained about six times as muchwater as enamel by volume. It is sometimes necessary to repeat thisoperation several times to remove all of the undersize material,depending on'the particle size distribution, but'the operation isreadily controlled by observing the progress of the settling period.

The sized particles are applied to the plate either by sifting or byspraying in a liquid medium containing a flotation agent and fired at1600 F. for 5 minutes. The sized particles fire uniformly to produce ahomogeneous coating free from air pockets and in the subsequent refiringafter application of the character marl:- ings the surface of the enamelremains un changed and no blistering or reboiling occurs. The describedmaterials and processes are suitable for producing all of the qualitiesdesired in a number plate with a single coating of enamel with resultanteconomies in production costs and the elimination of process defects.

Although the invention has'been described in I connection with themanufacture of number plates for telephone dials, it will be apparentthat it is equally applicable to other ornamented enameled articles andit is understood that the invention is limited only by the scope of theappended claims.

I claim:

l. A method of producing a contrastingly colored enamel coating on abase with an absence of reboiling comprising the steps of applying afinely divided vitreous enamel oi specified color on the base andexcluding particles that have been eliminated when the enamel is mixedwith a relatively larger volume of water and the supernatant liquid isdecanted after settling, fusing said enamel on the base, applying asecond enamel oi contrasting color to portions of the fused enamel, andrem-lag the base to fuse the second enamel.

2. A method oi producing a contrastingly colored enamel coating on aferrous base with an absence of reboiling comprising the steps ofapplying a finely divided vitreous enamel on the base, said enamel beingin the form of particles sumciently small to pass through a 120 meshscreen and excluding particles that have been eliminated when the enamelis m xed with about six times its volume of liquid and the supernatantliquid is decanted after settling, fusing said enamel on the base at aspecified temperature, applying a second enamel of contrasting color toportions of the'fused enamel, and refiring the base at a lowertemperature to fuse the second enamel.

3. A method of producing a contrastingly colored enamel coating on aferrous base with an absence of reboiling comprising the steps ofapplying a. lead hero-silicate enamel on the base, said enamel being inthe form of particles suifi- -ciently small to pass through a 120 meshscreen and excluding particles that are eliminated when the enamel ismixed with Water in the approximate proportions of one part of enamel tosix parts or water by volume and the supernatant water is decantedaitera settling period, fusing said enamel on the base at a temperatureof 11800" F., applying a mixture of enamel of contrasting color andlinseed oil to portions of the fused enamel in the form of characters,and refiring the base at a temperature around 1300 F. to mature thecharacters.

WALTER J. SCOTT.

CERTIFICATE OF CORRECTION. Patent No. 2,211,170. August 15, 191 0.

' WALTER J. SCOTT.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 1,second colfimn, lines 1).; and 16, for the word "used" read "fused"; andthat the said Letters Patent should be read with this correctionthereiri that the same may conform to the record 'of the case in thePatent Office.-

Signed and sealed this- 5th day of November, A. D. 191 0.

Henry, Va-n Arsdale (syeal) Acting Commissioner of Pa

